Cell interactions with the extracellular matrix (ECM) profoundly influence cell shape, migration, proliferation and differentiation - properties which are important for normal growth and development, and which affect many aspects of health care and disease including wound repair, angiogenesis, cancer metastasis, and atherogenesis. The mechanism by which the ECM influences cell behavior remains one of the basic unsolved problems in cell biology today. Recent evidence indicates that tyrosine- phosphorylation of proteins is a key event in the response. In support of this, a novel tyrosine kinase has been identified and shown to be localized to "focal adhesions," sites where interactions with the ECM occur via integrin receptors. Further studies indicate that this kinase, designated "Focal Adhesion Kinase" (FAK), becomes highly phosphorylated (on both tyrosine and serine sites) upon cell adhesion to fibronectin and other ECM substrates that bind to integrin receptors. These phosphorylation events are likely to be essential to an integrin-mediated signaling pathway involving FAK. The long term objective of the proposed work is to reach a full understanding of the role of FAK in bringing about ECM-influenced changes in cell behavior. Specifically, major sites of FAK phosphorylation induced upon the adherence of mouse fibroblasts to fibronectin will be determined by phosphopeptide mapping strategies, and the effect of these modifications on FAK's kinase activity, focal adhesion targeting, and ability to interact with known SH2-proteins will be evaluated. To gain further insight into FAK's signaling role, two molecular approaches will be undertaken to identify proteins that interact with FAK. One approach aims to identify novel SH2 proteins that interact with FAK phosphotyrosines. The other approach involves a powerful genetic screen for proteins that can stably interact with any part of the FAK molecule. Such proteins are likely to act as either upstream regulators or downstream effectors of FAK.